Control apparatus for internal combustion engine

ABSTRACT

An engine ECU executes a program including the steps of: calculating a fuel injection ratio of an in-cylinder injector; calculating an amount of spark advance using a first map employed when the in-cylinder injector has a fuel injection ratio of one, said first map providing a timing of ignition with a maximum amount of spark advance; calculating an amount of spark advance using a second map employed for a fuel injection ratio of zero, said second map providing a timing of ignition with a minimum amount of spark advance; and calculating an amount of spark advance using a third map employed for a fuel injection ratio larger than zero and smaller than one, said third map providing a timing of ignition with a larger amount of spark advance for a larger ratio.

This is a Division of application Ser. No. 11/342,665, filed Jan. 31,2006, which in turn is a nonprovisional application claiming the benefitof Japanese Patent Application No. 2005-078283 filed with the JapanPatent Office on Mar. 18, 2005. The disclosure of the prior applicationsis hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a control apparatus for an internalcombustion engine having a first fuel injection mechanism (anin-cylinder injector) for injecting a fuel into a cylinder and a secondfuel injection mechanism (an intake manifold injector) for injecting afuel into an intake manifold or an intake port, and relates particularlyto a technique for determining a timing of ignition with a fuelinjection ratio between the first and second fuel injection mechanismsconsidered.

2. Description of the Background Art

An internal combustion engine having an intake manifold injectorinjecting a fuel into an intake manifold of the engine and anin-cylinder injector injecting a fuel into a combustion chamber of theengine, and configured to stop fuel injection from the intake manifoldinjector when the engine load is lower than a preset load and to causefuel injection from the intake manifold injector when the engine load ishigher than the set load, is known.

In such an internal combustion engine, one configured to switch betweenstratified charge combustion and homogeneous combustion in accordancewith its operation state is known. In the stratified charge combustion,the fuel is injected from the in-cylinder injector during a compressionstroke to form a stratified air-fuel mixture locally around a sparkplug, for lean combustion of the fuel. In the homogeneous combustion,the fuel is diffused in the combustion chamber to form a homogeneousair-fuel mixture, for combustion of the fuel.

Japanese Patent Laying-Open No. 2001-020837 discloses a fuel injectioncontrol apparatus for an engine that switches between stratified chargecombustion and homogeneous combustion in accordance with an operationstate and that has a main fuel injection valve for injecting a fueldirectly into a combustion chamber and a secondary fuel injection valvefor injecting a fuel into an intake port of each cylinder. This fuelinjection control apparatus for the engine is characterized in that thefuel injection ratio between the main fuel injection valve and thesecondary fuel injection valve is set in a variable manner based on anoperation state of the engine.

According to this fuel injection control apparatus for the engine, thestratified charge combustion is carried out using only the main fuelinjection valve directly injecting the fuel into the combustion chamber,while the homogeneous combustion is carried out using both the main fuelinjection valve and the secondary fuel injection valve (or using onlythe secondary fuel injection valve in some cases). This can keep thecapacity of the main fuel injection valve small, even in the case of anengine of high power. Linearity in injection duration/injection quantitycharacteristic of the main fuel injection valve in a low-load regionsuch as during idling is improved, which in turn improves accuracy incontrol of the fuel injection quantity. Accordingly, it is possible tomaintain favorable stratified charge combustion, and thus to improvestability of the low-load operation such as idling. In the homogeneouscombustion, both the main and secondary fuel injection valves areemployed, so that the benefit of the direct fuel injection and thebenefit of the intake port injection are both enjoyed. Accordingly,favorable homogeneous combustion can also be maintained.

In the fuel injection control apparatus for the engine disclosed inJapanese Patent Laying-Open No. 2001-020837, the stratified chargecombustion and the homogeneous combustion are employed according to thesituations, which complicates ignition control, injection control andthrottle control, and requires control programs corresponding to therespective combustion manners. Particularly, upon switching between thecombustion manners, these controls require considerable changes, makingit difficult to realize desirable controls (of fuel efficiency, emissionpurification performance) at the time of transition. Further, in thestratified combustion region where lean combustion is carried out, thethree-way catalyst does not work, in which case a lean NOx catalystneeds to be used, leading to an increased cost.

Based on the foregoing, an engine has also been developed which does notprovide stratified charge combustion, and thus does not need control forswitching between the stratified charge combustion and the homogeneouscombustion and does not require an expensive lean NOx catalyst.

In controlling the engine to be ignited with its coolant having lowertemperature, spark advance is introduced for correction. This is becausewhen the coolant has lower temperature (poorer atomization is provided)lower combustion rates are provided and the engine is less prone toknock. The spark advance can provide an increased period of time betweenignition and exhaust, and despite lower combustion rates the air fuelmixture can sufficiently be combusted.

For a range having the in-cylinder and intake manifold injectors bearingshares, respectively, of injecting fuel, however, the in-cylinderinjector injects the fuel directly into the combustion chamber and thecombustion chamber can have an internal temperature significantlyeffectively reduced, whereas the intake manifold injector injects thefuel in the intake manifold and as a result the combustion chamber hasan internal temperature less effectively reduced. The fuel injectedthrough the in-cylinder injector reduces the combustion chamber'sinternal temperature to an extent, whereas that through the intakemanifold injector does so to a different extent. If the combustionchamber's temperature difference varies, anti-knock performance varies,and the combustion chamber's internal temperature is reduced andanti-knock performance is improved. If anti-knock performance varies, anoptimal timing of ignition varies. As such, using the coolant'stemperature alone to calculate an amount of spark advance cannot providean accurate timing of ignition (or an accurate amount of spark advance).Note that Japanese Patent Laying-open No. 2001-020837 only disclosesthat each injector is driven to achieve a fuel injection ratiocorresponding to the operation state of interest and a timing ofignition is set, and the document does not provide a solution to theproblem described above.

SUMMARY

An object of the present invention is to provide a control apparatus foran internal combustion engine having first and second fuel injectionmechanisms bearing shares, respectively, of injecting fuel into acylinder and an intake manifold, respectively, that can calculate anaccurate timing of ignition.

The present invention in one aspect provides a control apparatus for aninternal combustion engine having a first fuel injection mechanisminjecting fuel into a cylinder and a second fuel injection mechanisminjecting the fuel into an intake manifold. The control apparatusincludes: a controller controlling the first and second fuel injectionmechanisms to bear shares, respectively, of injecting the fuel at aratio calculated as based on a condition required for the internalcombustion engine, the ratio including preventing one of the fuelinjection mechanisms from injecting the fuel; and an ignition timingcontroller controlling an ignition device to vary a timing of ignition.The ignition timing controller controls the ignition device, as based ona reference timing of ignition of the internal combustion enginedetermined from the ratio.

In accordance with the present invention for a range having the firstfuel injection mechanism (e.g., an in-cylinder injector) and the secondfuel injection mechanism (e.g., an intake manifold injector) bearingshares, respectively, of injecting the fuel the fuel injected throughthe in-cylinder injector reduces the combustion chamber's internaltemperature. If the combustion chamber's internal temperature isreduced, anti-knock performance is enhanced, and a timing of ignitioncan be advanced. In contrast, the fuel injected through the intakemanifold injector reduces the combustion chamber's internal temperaturein a degree smaller than that through the in-cylinder injector does.Thus the internal combustion engine having two fuel injection mechanismsbearing shares, respectively, of injecting fuel, and reducing thecombustion chamber's internal temperature in different degrees,respectively, can achieve an accurately set timing of ignition. As aresult a control apparatus that can calculate an accurate timing ofignition can be provided for an internal combustion engine having firstand second fuel injection mechanisms bearing shares, respectively, ofinjecting fuel to inject the fuel into a cylinder and an intakemanifold, respectively, that are implemented by two types of fuelinjection mechanisms injecting fuel differently.

The present invention in another aspect provides a control apparatus foran internal combustion engine having a first fuel injection mechanisminjecting fuel into a cylinder and a second fuel injection mechanisminjecting the fuel into an intake manifold. The control apparatusincludes: a controller controlling the first and second fuel injectionmechanisms to bear shares, respectively, of injecting the fuel at aratio calculated as based on a condition required for the internalcombustion engine, the ratio including preventing one of the fuelinjection mechanisms from injecting the fuel; a storage storing areference timing of ignition; and an ignition timing controlleremploying the reference timing of ignition to control an ignitiondevice. The storage stores the reference timing of ignition calculatedas based on the ratio.

In accordance with the present invention the storage stores a referencetiming of ignition allowing a timing of ignition to be faster when thein-cylinder injector, which can reduce the combustion chamber's internaltemperature by its injected fuel in a large degree, has a higher fuelinjection ratio (including injecting fuel through the in-cylinderinjector alone) than when the intake manifold injector, which reducesthe combustion chamber's internal temperature by its injected fuel in asmall degree, has a higher fuel injection ratio (including injectingfuel through the intake manifold injector alone). Thus the internalcombustion engine having two fuel injection mechanisms bearing shares,respectively, of injecting fuel, and reducing the combustion chamber'sinternal temperature in different degrees, respectively, can achieve anaccurately set timing of ignition. As a result a control apparatus thatcan calculate an accurate timing of ignition can be provided for aninternal combustion engine having first and second fuel injectionmechanisms bearing shares, respectively, of injecting fuel to inject thefuel into a cylinder and an intake manifold, respectively, that areimplemented by two types of fuel injection mechanisms injecting fueldifferently.

Preferably the storage stores in a form of a map the reference timing ofignition previously calculated as based on the ratio.

In accordance with the present invention the reference timing ofignition can be determined from that stored in a map as based on a fuelinjection ratio of the in-cylinder and intake manifold injectors.

Still preferably, the storage stores the reference timing of ignitiondivided into a first map applied when the first fuel injection mechanismalone injects the fuel, a second map applied when the second fuelinjection mechanism alone injects the fuel, and a third map applied whenthe first and second fuel injection mechanisms inject the fuel.

In accordance with the present invention an in-cylinder injectorcorresponding to one example of the first fuel injection mechanism andan intake manifold injector corresponding to one example of the secondfuel injection mechanism that reduce the combustion chamber intemperature in different degrees, respectively, as they inject fuel,bear shares, respectively, of injecting fuel, and a reference timing ofignition is stored in a map divided into a first map applied when thein-cylinder injector alone injects the fuel, a second map applied whenthe intake manifold injector alone injects the fuel, and a third mapapplied when the in-cylinder and intake manifold injectors inject thefuel. A map can be selected as based on a fuel injection ratio betweenthe in-cylinder and intake manifold injectors to determine a storedreference timing of ignition.

Still preferably the first map provides the reference timing of ignitionset to provide spark advance.

In accordance with the present invention in the first map applied whenthe first fuel injection mechanism (e.g., an in-cylinder injector) aloneinjects fuel the fuel injected therethrough reduces the combustionchamber in temperature in a large degree and anti-knock performance isimproved. Accordingly the reference timing of ignition can be set to befaster.

Still preferably the second map provides the reference timing ofignition set to provide spark retard.

In accordance with the present invention in the second map applied whenthe first fuel injection mechanism (e.g., an intake manifold injector)alone injects fuel the fuel injected therethrough reduces the combustionchamber in temperature in a small degree and anti-knock performance isnot improved. Accordingly the reference timing of ignition is set to beslower.

Still preferably the third map provides the reference timing of ignitionset to provide spark advance when the first fuel injection mechanism isincreased in the ratio.

In accordance with the present invention when the first fuel injectionmechanism (e.g., the in-cylinder injector), which can reduce thecombustion chamber's internal temperature by its injected fuel in alarge degree, has a higher fuel injection ratio, anti-knock performancecan be better than when the second fuel injection mechanism (e.g., theintake manifold injector), which reduces the combustion chamber'sinternal temperature by its injected fuel in a small degree, has ahigher fuel injection ratio. As such, the reference timing of ignitioncan be advanced. Thus the internal combustion engine having two fuelinjection mechanisms that bear shares, respectively, of injecting fueland provide air fuel mixtures having different conditions, respectively,as they inject the fuel, can achieve an accurately set timing ofignition.

Still preferably the third map provides the reference timing of ignitionset to provide spark retard when the second fuel injection mechanism isincreased in the ratio.

In accordance with the present invention when the second fuel injectionmechanism (e.g., the intake manifold injector), which reduces thecombustion chamber in temperature by its injected fuel in a smalldegree, has a higher fuel injection ratio, anti-knock performance isless improved than when the first fuel injection mechanism (e.g., thein-cylinder injector), which can reduce the combustion chamber intemperature by its injected fuel in a large degree, has a higher fuelinjection ratio. Accordingly, the reference timing of ignition is set tobe slower. Thus the internal combustion engine having two fuel injectionmechanisms that bear shares, respectively, of injecting fuel and provideair fuel mixtures having different conditions, respectively, as theyinject the fuel, can achieve an accurately set timing of ignition.

Still preferably the first fuel injection mechanism is an in-cylinderinjector and the second fuel injection mechanism is an intake manifoldinjector.

In accordance with the present invention a control apparatus can beprovided that can calculate an accurate amount of spark advance for aninternal combustion engine having first and second fuel injectionmechanisms implemented by an in-cylinder injector and an intake manifoldinjector, respectively, separately provided and sharing injecting fuelwhen they share injecting the fuel in a cold state and a transitionalperiod from the cold state to a warm state.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematic configuration diagram of an engine system controlledby a control apparatus according to an embodiment of the presentinvention.

FIG. 2 is a flowchart (1) of a program executed by an engine ECU.

FIG. 3 shows an example of a map for shared injection.

FIG. 4 illustrates how the engine's operation state varies.

FIG. 5 is a flowchart (2) of a program executed by the engine ECU.

FIG. 6 is a diagram (1) representing a DI ratio map for a warm state ofan engine to which the present control apparatus is suitably applied.

FIG. 7 is a diagram (1) representing a DI ratio map for a cold state ofan engine to which the present control apparatus is suitably applied.

FIG. 8 is a diagram (2) representing a DI ratio map for a warm state ofan engine to which the present control apparatus is suitably applied.

FIG. 9 is a diagram (2) representing a DI ratio map for a cold state ofan engine to which the present control apparatus is suitably applied.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter reference will be made to the drawings to describe thepresent invention in an embodiment. In the following descriptionidentical components are identically denoted. They are also identical inname and function.

Note that while the following description is provided in conjunctionwith timing of ignition in a cold state and then refers to that forother than the cold state (as the combustion chamber's internaltemperature is reduced, anti knock performance is improved and a timingof ignition is accordingly advanced.)

Note that while the following description is provided exclusively inconjunction with spark advance in a cold state, the present invention isnot limited to such advance. The present invention also includes onceintroducing a spark advance and then a spark retard and introducing aspark retard from a reference timing of ignition. Furthermore, arelationship between a smaller spark advance for a higher ratio of fuelinjected through an in-cylinder injector and a significantly large sparkadvance for a higher ratio of fuel injected through an intake manifoldinjector, can be inverted. For example if the performance of anin-cylinder injector 100 as a discrete injector and that of an intakemanifold injector 120 as a discrete injector contribute to lesssufficient atomization of the fuel injected through in-cylinder injector100 than that of the fuel injected through intake manifold injector 120for the same engine coolant temperature THW, the fuel injectionratio-spark advance relationship described above can be inverted.

FIG. 1 is a schematic configuration diagram of an engine system that iscontrolled by an engine ECU (Electronic Control Unit) implementing thecontrol apparatus for an internal combustion engine according to anembodiment of the present invention. In FIG. 1, an in-line 4-cylindergasoline engine is shown, although the application of the presentinvention is not restricted to such an engine.

As shown in FIG. 1, the engine 10 includes four cylinders 112, eachconnected via a corresponding intake manifold 20 to a common surge tank30. Surge tank 30 is connected via an intake duct 40 to an air cleaner50. An airflow meter 42 is arranged in intake duct 40, and a throttlevalve 70 driven by an electric motor 60 is also arranged in intake duct40. Throttle valve 70 has its degree of opening controlled based on anoutput signal of an engine ECU 300, independently from an acceleratorpedal 100. Each cylinder 112 is connected to a common exhaust manifold80, which is connected to a three-way catalytic converter 90.

Each cylinder 112 is provided with an in-cylinder injector 110 injectingfuel into the cylinder and an intake manifold injector 120 injectingfuel into an intake port or/and an intake manifold. Injectors 110 and120 are controlled based on output signals from engine ECU 300. Further,in-cylinder injector 110 of each cylinder is connected to a common fueldelivery pipe 130. Fuel delivery pipe 130 is connected to ahigh-pressure fuel pump 150 of an engine-driven type, via a check valve140 that allows a flow in the direction toward fuel delivery pipe 130.In the present embodiment, an internal combustion engine having twoinjectors separately provided is explained, although the presentinvention is not restricted to such an internal combustion engine. Forexample, the internal combustion engine may have one injector that caneffect both in-cylinder injection and intake manifold injection.

As shown in FIG. 1, the discharge side of high-pressure fuel pump 150 isconnected via an electromagnetic spill valve 152 to the intake side ofhigh-pressure fuel pump 150. As the degree of opening of electromagneticspill valve 152 is smaller, the quantity of the fuel supplied fromhigh-pressure fuel pump 150 into fuel delivery pipe 130 increases. Whenelectromagnetic spill valve 152 is fully open, the fuel supply fromhigh-pressure fuel pump 150 to fuel delivery pipe 130 is stopped.Electromagnetic spill valve 152 is controlled based on an output signalof engine ECU 300.

Each intake manifold injector 120 is connected to a common fuel deliverypipe 160 on a low pressure side. Fuel delivery pipe 160 andhigh-pressure fuel pump 150 are connected via a common fuel pressureregulator 170 to a low-pressure fuel pump 180 of an electricmotor-driven type. Further, low-pressure fuel pump 180 is connected viaa fuel filter 190 to a fuel tank 200. Fuel pressure regulator 170 isconfigured to return a part of the fuel discharged from low-pressurefuel pump 180 back to fuel tank 200 when the pressure of the fueldischarged from low-pressure fuel pump 180 is higher than a preset fuelpressure. This prevents both the pressure of the fuel supplied to intakemanifold injector 120 and the pressure of the fuel supplied tohigh-pressure fuel pump 150 from becoming higher than theabove-described preset fuel pressure.

Engine ECU 300 is implemented with a digital computer, and includes aROM (Read Only Memory) 320, a RAM (Random Access Memory) 330, a CPU(Central Processing Unit) 340, an input port 350, and an output port360, which are connected to each other via a bidirectional bus 310.

Airflow meter 42 generates an output voltage that is proportional to anintake air quantity, and the output voltage is input via an A/Dconverter 370 to input port 350. A coolant temperature sensor 380 isattached to engine 10, and generates an output voltage proportional to acoolant temperature of the engine, which is input via an A/D converter390 to input port 350.

A fuel pressure sensor 400 is attached to fuel delivery pipe 130, andgenerates an output voltage proportional to a fuel pressure within fueldelivery pipe 130, which is input via an A/D converter 410 to input port350. An air-fuel ratio sensor 420 is attached to an exhaust manifold 80located upstream of three-way catalytic converter 90. Air-fuel ratiosensor 420 generates an output voltage proportional to an oxygenconcentration within the exhaust gas, which is input via an A/Dconverter 430 to input port 350.

Air-fuel ratio sensor 420 of the engine system of the present embodimentis a full-range air-fuel ratio sensor (linear air-fuel ratio sensor)that generates an output voltage proportional to the air-fuel ratio ofthe air-fuel mixture burned in engine 10. As air-fuel ratio sensor 420,an O₂ sensor may be employed, which detects, in an on/off manner,whether the air-fuel ratio of the air-fuel mixture burned in engine 10is rich or lean with respect to a theoretical air-fuel ratio.

Accelerator pedal 100 is connected with an accelerator pedal positionsensor 440 that generates an output voltage proportional to the degreeof press down of accelerator pedal 100, which is input via an A/Dconverter 450 to input port 350. Further, an engine speed sensor 460generating an output pulse representing the engine speed is connected toinput port 350. ROM 320 of engine ECU 300 prestores, in the form of amap, values of fuel injection quantity that are set in association withoperation states based on the engine load factor and the engine speedobtained by the above-described accelerator pedal position sensor 440and engine speed sensor 460, and correction values thereof set based onthe engine coolant temperature.

With reference to the flowchart of FIG. 2 engine ECU 300 of FIG. 1executes a program having a structure for control, as describedhereinafter.

In step (S) 100 engine ECU 300 employs a map as shown in FIG. 3 tocalculate an injection ratio of in-cylinder injector 110. Hereinafterthis ratio will be referred to as “DI ratio r,” wherein 0≦r≦1. The mapused to calculate the ratio will be described later.

In S100 engine ECU 300 determines whether DI ratio r is 1, 0, or largerthan 0 and smaller than 1. If DI ratio r is 1 (r=1.0 in S110) theprocess proceeds to S120. If DI ratio r is 0 (r=0 in S110) the processproceeds to S130. If DI ratio r is larger than 0 and smaller than 1(0≦r≦1 in S110) the process proceeds to S140.

In S120 engine ECU 300 calculates an amount of cold state spark advancecorresponding to that of spark advance for correction in a cold statewhen in-cylinder injector 110 alone injects fuel. This is done forexample by employing a function f(1) to calculate an amount of coldstate spark advance=f(1)(THW). Note that “THW” represents thetemperature of a coolant of engine 10 as detected by coolant temperaturesensor 380.

In S130 engine ECU 300 calculates an amount of cold state spark advancecorresponding to that of spark advance for correction in the cold statewhen intake manifold injector 120 alone injects fuel. This is done forexample by employing a function f(2) to calculate an amount of coldstate spark advance=f(2)(THW).

In S140 engine ECU 300 calculates an amount of cold state spark advancecorresponding to that of spark advance for correction in a cold statewhen in-cylinder and intake manifold injectors 110 and 120 bear shares,respectively, of injecting fuel. This is done for example by employing afunction f(3) to calculate an amount of cold state sparkadvance=f(3)(THW, r). Note that “r” represents a DI ratio.

In S150 engine ECU 300 calculates a timing of ignition for example byemploying a function g to calculate a timing of ignition=g (an amount ofcold state spark advance).

Reference will now be made to FIG. 3 to describe an injection ratio(0≦DI ratio r≦1) of in-cylinder injector 110 with an engine speed NE anda load factor KL of engine 10 serving as parameters.

In a low engine speed and high load range the fuel injected throughin-cylinder injector 110 is insufficiently mixed with air, and in thecombustion chamber the air fuel mixture tends to be inhomogeneous andthus provide unstable combustion. Accordingly, for this range, DI ratior is reduced to increase an injection ratio (1-r) of intake manifoldinjector 120 to sufficiently mix the air fuel mixture before it isintroduced into the combustion chamber.

In a high engine speed and low load range the air fuel mixture injectedthrough in-cylinder injector 110 is readily homogenized. Accordingly, DIratio r is increased. The fuel injected through in-cylinder injector 110is vaporized within the combustion chamber involving latent heat ofvaporization (by absorbing heat from the combustion chamber).Accordingly at the compression side the air fuel mixture is decreased intemperature and improved antiknock performance is provided. Furthermore,as the combustion chamber is decreased in temperature, improved intakeefficiency can be achieved and high power output expected. Furthermore,in-cylinder injector 110 can have its end, exposed in the combustionchamber, cooled by the fuel and thus have its injection hole preventedfrom having deposit adhering thereto.

As based on the configuration and flowchart as described above, engine10 in the present embodiment operates as described hereinafter. Notethat in the following description “if the engine's coolant varies intemperature” and other similar expressions indicate a transitionalperiod from a cold state to a warm state.

No Variation in DI Ratio and Variation Present in Temperature of Coolantfor Engine

When engine 10 starts, normally the coolant increases in temperature.More specifically, in FIG. 4, the coolant increases in temperature froma temperature TH(1) corresponding to a point A to a temperature TH(2)corresponding to a point B. The DI ratio is calculated (S100) and if DIratio r is not found to have varied (e.g., r=0.7) a decision is madethat it is larger than 0 and smaller than 1 (0<r<1.0 in S110) andfunction f(3) is accordingly used to calculate an amount of cold statespark advance by f(3) (THW, r) (S140).

In FIG. 4, for point A, by f(3) (TH(1), r), wherein r=0.7, an amount ofcold state spark advance is calculated as a spark advance for correction(1). With the amount of cold state spark advance set at the sparkadvance for correction (1), engine 10 is operated, and temperature THWincreases from TH(1) to TH(2) to reach point B. For point B, by f(3)(TH(2), r), wherein r=0.7, an amount of cold state spark advance iscalculated as a spark advance for correction (2). In other words, anamount of spark advance for correction is reduced from the spark advancefor correction (1) to the spark advance for correction (2) by avariation in amount of spark advance for correction, which is providedby the spark advance for correction (1) minus the spark advance forcorrection (2).

Variation Present in DI Ratio and No Variation in Temperature of Coolantfor Engine

While engine 10 is started, the coolant may not vary depending on thevehicle's surrounding (temperature in particular). If in such a case theengine 10 operation state varies and DI ratio r drops from 0.7, i.e., inFIG. 4, while temperature TH(1) corresponding to point A is held, apoint C allowing DI ratio r smaller than 0.7 is attained (or it may bevice versa). The DI ratio is calculated (S100) and if DI ratio r isfound to have varied (for example from 0.7 to 0.5) a decision is madethat DI ratio r is still larger than 0 and smaller than 1 (0<r<1.0 inS110), and function f(3) is employed to calculate an amount of coldstate spark advance by f(3) (THW, r) (S140).

In FIG. 4, for point A, by f(3) (TH(1), r), wherein r=0.7, an amount ofcold state spark advance is calculated. In this condition engine 10 isoperated, and while temperature THW is held at TH(1), DI ratio rdecreases to reach point C. For point C, by f(3) (TH(1), r), whereinr=0.5, an amount of cold state spark advance is calculated. Morespecifically, a spark advance is introduced by a variation in amount ofspark advance for correction. This indicates that a larger spark advanceis introduced as the port's temperature is lower than the cylinder'sinternal temperature and the fuel injected through intake manifoldinjector 120 is hard to atomize.

Variation Present in DI Ratio and Variation Present in Temperature ofCoolant for Engine

When engine 10 is started the coolant's temperature and DI ratio r mayboth vary. In such a case, in FIG. 4 point A corresponding totemperature TH(1) and DI ratio r=0.7 transitions to a point Dcorresponding to temperature TH(2) higher than TH(1) and a DI ratio rsmaller than 0.7. The DI ratio is calculated (S100) and if DI ratio r isfound to have varied (for example from 0.7 to 0.5) a decision is stillmade that DI ratio r is larger than 0 and smaller than 1 (0<r<1.0 inS110), and function f(3) is employed to calculate an amount of coldstate spark advance by f(3) (THW, r) (S140).

In FIG. 4, for point A, by f(3) (TH(1), r), wherein r=0.7, an amount ofcold state spark advance is calculated. In this condition engine 10 isoperated, and while temperature THW changes from TH(1) to TH(2) the DIratio also decreases to reach point D. For point D, by f(3) (TH(2), r),wherein r=0.5, an amount of cold state spark advance is calculated. Morespecifically, a timing of ignition is varied by a variation in amount ofspark advance for correction. This indicates that when a DI ratio isneither 0 nor 1 an amount of cold state spark advance is calculated by afunction of the coolant's temperature and DI ratio r, and a variation inamount of spark advance for correction also depends on those of thecoolant in temperature and DI ratio r, respectively.

Thus in a cold state and a transitional period from the cold state to awarm state when an in-cylinder injector and an intake manifold injectorbear shares, respectively, of injecting fuel, not only temperature THWof the coolant of the engine but DI ratio r is also used to calculate anamount of cold state spark advance. If the cylinder's interior and theport are different in temperature and thus have fuel therein atomizeddifferently an accurate spark advance can be provided to combust thefuel satisfactorily.

Map of Reference Timing of Ignition Depending on Fuel Injection Ratiothat is not Limited to Cold State

Hereinafter will be described an embodiment that is not limited to lowtemperature of engine 10, or cold state. In the present embodimentin-cylinder injector 110 has a fuel injection ratio or DI ratio rdivided into three values, i.e., r=0, r=1, and 0<r<1, and a referencetiming of ignition is accordingly, previously stored in engine ECU 300at ROM 320, RAM 340 or the like.

Fuel injected through in-cylinder injector 110 and that through intakemanifold injector 120 decrease the combustion chamber in temperature insignificantly different degrees, respectively. More specifically, theformer, which is injected directly into the combustion chamber, and thelatter, which is injected in the intake manifold and introduced into thecombustion chamber, decrease the combustion chamber in temperaturedifferently. More specifically, the latter decreases the combustionchamber in temperature in a small degree, whereas the former, injecteddirectly into the combustion chamber, decreases the combustion chamberin temperature in a large degree. When the combustion chamber has lowtemperature, anti knock performance can be improved, and a timing ofignition can be set to be advanced.

A first map is set as a map applied for DI ratio r=1 (i.e., whenin-cylinder injector 110 alone injects fuel) for a reference timing ofignition that allows a timing of ignition to be maximally advanced. Fuelinjected through in-cylinder injector 110 decreases the combustionchamber in temperature maximally, and anti-knock performance canmaximally be improved. The timing of ignition can be advanced and engine10 can satisfactorily exhibit its characteristic(s).

A second map is set as a map applied for DI ratio r=0 (i.e., when intakemanifold injector 120 alone injects fuel) for a reference timing ofignition that allows a timing of ignition to be maximally retarded. Fuelinjected through intake manifold injector 120 decrease the combustionchamber in temperature in a small degree. From such decreasedtemperature of the combustion chamber, improved anti-knock performanceis hardly expected. Accordingly the timing of ignition is retarded toprevent the engine from knocking.

A third map is set as a map applied for DI ratio r larger than 0 andsmaller than 1 (i.e., when in-cylinder injector 110 and intake manifoldinjector 120 bear shares, respectively, of injecting fuel) for areference timing of ignition that allows a timing of ignition to beadvanced for higher DI ratios. As DI ratio r increases, in-cylinderinjector 110 injects more fuel and the combustion chamber is accordinglydecreased in temperature in a larger degree. Anti-knock performance canbe improved, and the timing of ignition can be advanced.

Engine ECU 300 prepares three maps for such reference timings ofignition, and in accordance with a ratio of in-cylinder injector 110bearing a share of injecting fuel, or DI ratio r, selects one of themaps to switch a map of a reference timing of ignition. In accordancewith the selected map engine ECU 300 calculates a reference timing ofignition. In particular, the third map provides a reference timing ofignition varied by DI ratio r. Accordingly, not only the map but afunction interpolating an intermediate portion set in the map may alsobe previously calculated and stored, and used to provide interpolation.

With reference to the FIG. 5 flowchart the FIG. 1 engine ECU 300executes a program having a structure for control, as describedhereinafter. Note that in the FIG. 5 flowchart, the steps identical tothose of the FIG. 2 flowchart are identically labeled.

At S220 engine ECU 300 calculates in accordance with the first mapcorresponding to DI ratio r=1 an amount of spark advance with anti-knockperformance considered.

At S230 engine ECU 300 calculates in accordance with the second mapcorresponding to DI ratio r=0 an amount of spark advance with anti-knockperformance considered.

At S240 engine ECU 300 calculates in accordance with the third mapcorresponding to 0<DI ratio r<1 an amount of spark advance withanti-knock performance considered. More specifically for examplefunction F(3) is used to calculate an amount of spark advance=F(3)(r)with anti-knock performance considered, wherein r represents a DI ratio.

At S250 engine ECU 300 calculates a timing of ignition. Morespecifically for example function G is used to calculate the timing ofignition=G (an amount of spark advance with anti-knock performanceconsidered).

Thus, not only for cold state, three maps (DI ratio r=1, 0, or largerthan 0 and smaller than 1) can be selected in accordance with DI ratio rand the selected map used to calculate a reference timing of ignition.This allows an appropriate reference timing of ignition to be calculatedcorresponding to DI ratio r. Thus an optimal reference timing ofignition can be set corresponding to DI ratio r, and detrimentsattributed to excessive spark retard and advance can be prevented.

Engine (1) Suitable for Application of the Control Apparatus

An engine (1) suitable for application of the control apparatus in thepresent embodiment will be described hereinafter.

Referring to FIGS. 6 and 7, maps each indicating a fuel injection ratiobetween in-cylinder injector 110 and intake manifold injector 120,identified as information associated with an operation state of engine10, will now be described. Herein, the fuel injection ratio between thetwo injectors will also be expressed as a ratio of the quantity of thefuel injected from in-cylinder injector 110 to the total quantity of thefuel injected, which is referred to as the “fuel injection ratio ofin-cylinder injector 110”, or, a “DI (Direct Injection) ratio (r)”. Themaps are stored in ROM 320 of engine ECU 300. FIG. 6 shows the map forthe warm state of engine 10, and FIG. 7 shows the map for the cold stateof engine 10.

In the maps shown in FIGS. 6 and 7, with the horizontal axisrepresenting an engine speed of engine 10 and the vertical axisrepresenting a load factor, the fuel injection ratio of in-cylinderinjector 110, or the DI ratio r, is expressed in percentage.

As shown in FIGS. 6 and 7, the DI ratio r is set for each operationregion that is determined by the engine speed and the load factor ofengine 10. “DI RATIO r=100%” represents the region where fuel injectionis carried out using only in-cylinder injector 110, and “DI RATIO r=0%”represents the region where fuel injection is carried out using onlyintake manifold injector 120. “DI RATIO r≠0%”, “DI RATIO r≠100%” and“0%<DI RATIO r<100%” each represent the region where fuel injection iscarried out using both in-cylinder injector 110 and intake manifoldinjector 120. Generally, in-cylinder injector 110 contributes to anincrease of output performance, while intake manifold injector 120contributes to uniformity of the air-fuel mixture. These two kinds ofinjectors having different characteristics are appropriately selecteddepending on the engine speed and the load factor of engine 10, so thatonly homogeneous combustion is conducted in the normal operation stateof engine 10 (other than the abnormal operation state such as a catalystwarm-up state during idling, for example).

Further, as shown in FIGS. 6 and 7, the fuel injection ratio betweenin-cylinder injector 110 and intake manifold injector 120 is defined asthe DI ratio r, individually in the maps for the warm state and the coldstate of the engine. The maps are configured to indicate differentcontrol regions of in-cylinder injector 110 and intake manifold injector120 as the temperature of engine 10 changes. When the temperature ofengine 10 detected is equal to or higher than a predeterminedtemperature threshold value, the map for the warm state shown in FIG. 6is selected; otherwise, the map for the cold state shown in FIG. 7 isselected. One or both of in-cylinder injector 110 and intake manifoldinjector 120 are controlled based on the selected map and according tothe engine speed and the load factor of engine 10.

The engine speed and the load factor of engine 10 set in FIGS. 6 and 7will now be described. In FIG. 6, NE(1) is set to 2500 rpm to 2700 rpm,KL(1) is set to 30% to 50%, and KL(2) is set to 60% to 90%. In FIG. 7,NE(3) is set to 2900 rpm to 3100 rpm. That is, NE(1)<NE(3). NE(2) inFIG. 6 as well as KL(3) and KL(4) in FIG. 7 are also set as appropriate.

When comparing FIG. 6 and FIG. 7, NE(3) of the map for the cold stateshown in FIG. 7 is greater than NE(1) of the map for the warm stateshown in FIG. 6. This shows that, as the temperature of engine 10 islower, the control region of intake manifold injector 120 is expanded toinclude the region of higher engine speed. That is, when engine 10 iscold, deposits are unlikely to accumulate in the injection hole ofin-cylinder injector 110 (even if the fuel is not injected fromin-cylinder injector 110). Thus, the region where the fuel injection isto be carried out using intake manifold injector 120 can be expanded, tothereby improve homogeneity.

When comparing FIG. 6 and FIG. 7, “DI RATIO r=100%” holds in the regionwhere the engine speed of engine 10 is equal to or higher than NE(1) inthe map for the warm state, and in the region where the engine speed isNE(3) or higher in the map for the cold state. Further, “DI RATIOr=100%” holds in the region where the load factor is KL(2) or greater inthe map for the warm state, and in the region where the load factor isKL(4) or greater in the map for the cold state. This means that fuelinjection is carried out using only in-cylinder injector 110 in theregion where the engine speed is at a predetermined high level, and thatfuel injection is carried out using only in-cylinder injector 110 in theregion where the engine load is at a predetermined high level, since forthe high speed region and the low load region the engine 10 speed andload are high and a large quantity of air is intaken, and in-cylinderinjector 110 can singly be used to inject fuel to provide a homogeneousair fuel mixture. In this case, the fuel injected from in-cylinderinjector 110 is atomized within the combustion chamber involving latentheat of vaporization (by absorbing heat from the combustion chamber).Accordingly, the temperature of the air-fuel mixture is decreased at thecompression side, and thus, the antiknock performance improves. Further,with the temperature of the combustion chamber decreased, intakeefficiency improves, leading to high power output.

In the map for the warm state in FIG. 6, fuel injection is also carriedout using only in-cylinder injector 110 when the load factor is KL(1) orless. This shows that in-cylinder injector 110 alone is used in apredetermined low load region when the temperature of engine 10 is high.When engine 10 is in the warm state, deposits are likely to accumulatein the injection hole of in-cylinder injector 110. However, when fuelinjection is carried out using in-cylinder injector 110, the temperatureof the injection hole can be lowered, whereby accumulation of depositsis prevented. Further, clogging of in-cylinder injector 110 may beprevented while ensuring a minimum fuel injection quantity thereof.Thus, in-cylinder injector 110 alone is used in the relevant region.

When comparing FIG. 6 and FIG. 7, there is a region of “DI RATIO r=0%”only in the map for the cold state in FIG. 7. This shows that fuelinjection is carried out using only intake manifold injector 120 in apredetermined low load region (KL(3) or less) when the temperature ofengine 10 is low. When engine 10 is cold and low in load and the intakeair quantity is small, atomization of the fuel is unlikely to occur. Insuch a region, it is difficult to ensure favorable combustion with thefuel injection from in-cylinder injector 110. Further, particularly inthe low-load and low-speed region, high power output using in-cylinderinjector 110 is unnecessary. Accordingly, fuel injection is carried outusing intake manifold injector 120 alone, rather than using in-cylinderinjector 110, in the relevant region.

Further, in an operation other than the normal operation, i.e., in thecatalyst warm-up state at idle of engine 10 (abnormal operation state),in-cylinder injector 110 is controlled to carry out stratified chargecombustion. By causing the stratified charge combustion during thecatalyst warm-up operation, warming up of the catalyst is promoted, andexhaust emission is thus improved.

Engine (2) Suitable for Application of the Control Apparatus

An engine (2) suitable for application of the control apparatus in thepresent embodiment will be described hereinafter. In the followingdescription of engine (2) the same description as that of engine (1)will not be repeated.

Referring to FIGS. 8 and 9, maps each indicating a fuel injection ratiobetween in-cylinder injector 110 and intake manifold injector 120,identified as information associated with an operation state of engine10, will now be described. The maps are stored in ROM 320 of engine ECU300. FIG. 8 shows the map for the warm state of engine 10, and FIG. 9shows the map for the cold state of engine 10.

When comparing FIG. 8 and FIG. 9, the figures differ from FIGS. 6 and 7,as follows: “DI RATIO r=100%” holds in the region where the engine speedof engine 10 is equal to or higher than NE(1) in the map for the warmstate, and in the region where the engine speed is NE(3) or higher inthe map for the cold state. Further, except for the low-speed region,“DI RATIO r=100%” holds in the region where the load factor is KL(2) orgreater in the map for the warm state, and in the region where the loadfactor is KL(4) or greater in the map for the cold state. This meansthat fuel injection is carried out using only in-cylinder injector 110in the region where the engine speed is at a predetermined high level,and that fuel injection is often carried out using only in-cylinderinjector 110 in the region where the engine load is at a predeterminedhigh level. However, in the low-speed and high-load region, mixing of anair-fuel mixture formed by the fuel injected from in-cylinder injector110 is poor, and such inhomogeneous air-fuel mixture within thecombustion chamber may lead to unstable combustion. Accordingly, thefuel injection ratio of in-cylinder injector 110 is increased as theengine speed increases where such a problem is unlikely to occur,whereas the fuel injection ratio of in-cylinder injector 110 isdecreased as the engine load increases where such a problem is likely tooccur. These changes in the fuel injection ratio of in-cylinder injector110, or, the DI ratio r, are shown by crisscross arrows in FIGS. 8 and9. In this manner, variation in output torque of the engine attributableto the unstable combustion can be suppressed. It is noted that thesemeasures are approximately equivalent to the measures to decrease thefuel injection ratio of in-cylinder injector 110 as the state of theengine moves toward the predetermined low speed region, or to increasethe fuel injection ratio of in-cylinder injector 110 as the engine statemoves toward the predetermined low load region. Further, except for therelevant region (indicated by the crisscross arrows in FIGS. 8 and 9),in the region where fuel injection is carried out using only in-cylinderinjector 110 (on the high speed side and on the low load side), ahomogeneous air-fuel mixture is readily obtained even when the fuelinjection is carried out using only in-cylinder injector 110. In thiscase, the fuel injected from in-cylinder injector 110 is atomized withinthe combustion chamber involving latent heat of vaporization (byabsorbing heat from the combustion chamber). Accordingly, thetemperature of the air-fuel mixture is decreased at the compressionside, and thus, the antiknock performance improves. Further, with thetemperature of the combustion chamber decreased, intake efficiencyimproves, leading to high power output.

In engine 10 described with reference to FIGS. 6-9, homogeneouscombustion is achieved by setting the fuel injection timing ofin-cylinder injector 110 in the intake stroke, while stratified chargecombustion is achieved by setting it in the compression stroke. That is,when the fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, a rich air-fuel mixture can be located locallyaround the spark plug, so that a lean air-fuel mixture in the combustionchamber as a whole is ignited to realize the stratified chargecombustion. Even if the fuel injection timing of in-cylinder injector110 is set in the intake stroke, stratified charge combustion can berealized if it is possible to locate a rich air-fuel mixture locallyaround the spark plug.

As used herein, the stratified charge combustion includes both thestratified charge combustion and semi-stratified charge combustion. Inthe semi-stratified charge combustion, intake manifold injector 120injects fuel in the intake stroke to generate a lean and homogeneousair-fuel mixture in the whole combustion chamber, and then in-cylinderinjector 110 injects fuel in the compression stroke to generate a richair-fuel mixture around the spark plug, so as to improve the combustionstate. Such semi-stratified charge combustion is preferable in thecatalyst warm-up operation for the following reasons. In the catalystwarm-up operation, it is necessary to considerably retard the ignitiontiming and maintain favorable combustion state (idling state) so as tocause a high-temperature combustion gas to reach the catalyst. Further,a certain quantity of fuel needs to be supplied. If the stratifiedcharge combustion is employed to satisfy these requirements, thequantity of the fuel will be insufficient. With the homogeneouscombustion, the retarded amount for the purpose of maintaining favorablecombustion is small compared to the case of stratified chargecombustion. For these reasons, the above-described semi-stratifiedcharge combustion is preferably employed in the catalyst warm-upoperation, although either of stratified charge combustion andsemi-stratified charge combustion may be employed.

Furthermore in the engine described with reference to FIGS. 6-9preferably in-cylinder injector 110 is timed to inject fuel at thecompression stroke for the following reason, although in engine 10described above, the fuel injection timing of in-cylinder injector 110is set in the intake stroke in a basic region corresponding to thealmost entire region (herein, the basic region refers to the regionother than the region where semi-stratified charge combustion isconducted by causing intake manifold injector 120 to inject the fuel inthe intake stroke and causing in-cylinder injector 110 to inject thefuel in the compression stroke, which is conducted only in the catalystwarm-up state). The fuel injection timing of in-cylinder injector 110,however, may be set temporarily in the compression stroke for thepurpose of stabilizing combustion, for the following reasons.

When the fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, the air-fuel mixture is cooled by the injected fuelwhile the temperature in the cylinder is relatively high. This improvesthe cooling effect and, hence, the antiknock performance. Further, whenthe fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, the time from the fuel injection to the ignition isshort, which ensures strong penetration of the injected fuel, so thatthe combustion rate increases. The improvement in antiknock performanceand the increase in combustion rate can prevent variation in combustion,and thus, combustion stability is improved.

Note that in the above described flowchart at S150 and S250 whenever theflowchart is executed a reference timing of ignition may be calculatedfrom the engine 10 operation state and function g correcting thereference timing of ignition by an amount of cold state spark advancemay be used to calculate a timing of ignition.

Furthermore, irrespectively of the engine 10 temperature (i.e., ineither a warm state or a cold state) when idling is off (i.e., an idleswitch is off, the accelerator pedal is pressed) the FIG. 6 or 8 map fora warm state may be used. (Regardless of cold or warm state, in-cylinderinjector 110 is used for a low load range.)

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A control apparatus for an internal combustion engine having a firstfuel injection mechanism injecting fuel into a cylinder and a secondfuel injection mechanism injecting the fuel into an intake manifold,comprising: a controller controlling said first and second fuelinjection mechanisms to bear shares, respectively, of injecting the fuelat a ratio calculated as based on a condition required for said internalcombustion engine; a storage storing a reference timing of ignition; andan ignition timing controller always employing at least said referencetiming of ignition to control an ignition device, wherein said first andsecond fuel injection mechanisms bear shares, respectively, of injectingthe fuel; wherein said storage stores said reference timing of ignitionto provide spark advance when said first fuel injection mechanism isincreased in said ratio; wherein said storage stores in a form of a mapsaid reference timing of ignition previously calculated as based on saidratio; and wherein said storage stores said reference timing of ignitiondivided into a first map applied when said first fuel injectionmechanism alone injects the fuel, a second map applied when said secondfuel injection mechanism alone injects the fuel, and a third map appliedwhen said first and second fuel injection mechanisms inject the fuel. 2.The control apparatus according to claim 1, wherein said first mapprovides said reference timing of ignition set to provide spark advance.3. The control apparatus according to claim 1, wherein said second mapprovides said reference timing of ignition set to provide spark retard.4. The control apparatus according to claim 1, wherein said third mapprovides said reference timing of ignition set to provide spark retardwhen said second fuel injection mechanism is increased in said ratio. 5.A control apparatus for an internal combustion engine having first fuelinjection means for injecting fuel into a cylinder and second fuelinjection means for injecting the fuel into an intake manifold,comprising: control means for controlling said first and second fuelinjection means to bear shares, respectively, of injecting the fuel at aratio calculated as based on a condition required for said internalcombustion engine, said ratio including preventing one of said fuelinjection means from injecting the fuel; storage means for storing areference timing of ignition; and ignition timing control means alwaysemploying at least said reference timing of ignition for controlling anignition device, wherein said first and second fuel injection means bearshares, respectively, of injecting the fuel; wherein said storage meansincludes means for storing said reference timing of ignition calculatedas to provide spark advance when said first fuel injection means isincreased based on said ratio; wherein said storage means includes meansfor storing in a form of a map said reference timing of ignitionpreviously calculated as based on said ratio; and wherein said storagemeans includes means for storing said reference timing of ignitiondivided into a first map applied when said first fuel injection meansalone injects the fuel, a second map applied when said second fuelinjection means alone injects the fuel, and a third map applied whensaid first and second fuel injection means inject the fuel.
 6. Thecontrol apparatus according to claim 5, wherein said first map providessaid reference timing of ignition set to provide spark advance.
 7. Thecontrol apparatus according to claim 5, wherein said second map providessaid reference timing of ignition set to provide spark retard.
 8. Thecontrol apparatus according to claim 5, wherein said third map providessaid reference timing of ignition set to provide spark retard when saidsecond fuel injection means is increased in said ratio.